Mechanical Engineering
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Item AN INTEGRATED, MULTI-PHYSICS ANALYSIS AND DESIGN OPTIMIZATION FRAMEWORK FOR AIR-TO-REFRIGERANT HEAT EXCHANGERS WITH SHAPE-OPTIMIZED TUBES(2022) Tancabel, James M; Radermacher, Reinhard; Aute, Vikrant; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Air-to-fluid Heat eXchangers (HX) are fundamental components of many systems we encounter in our daily lives, from Heating, Ventilation, Air-Conditioning and Refrigeration (HVAC&R) systems to electronics cooling, automotive, power plants, and aviation applications. The importance of HXs is evident in the level of investment devoted to HX innovation in recent years. While current state-of-the-art HXs have adequately addressed past challenges, ever-increasing energy demands and increasingly stringent global energy standards require novel tools and methodologies which can quickly and efficiently develop the next generation of high-performance HXs. In recent years, advancements in computational tools and advanced manufacturing technologies have enabled engineers to consider small characteristic diameter HX tubes with novel shapes and topologies which were not feasible even a decade ago. These small diameter, shape-optimized tubes have been shown to perform the same job as existing HXs while offering significant and desirable improvements in performance metrics such as envelope volume, face area, weight, and refrigerant charge. However, the structural integrity of shape-optimized tubes was often guaranteed by utilizing conservative tube thicknesses to ensure equipment safety, prevent refrigerant leakages, and satisfy product qualification requirements, resulting in increased material consumption and manufacturer costs while reducing the likelihood of industry acceptance for the new technology. Additionally, the actual HX operating conditions are often different from design conditions, resulting in significant performance degradations. For example, novel HX design is typically assumes uniform normal airflow on the HX face area even though HXs in HVAC&R applications rarely experience such flows, and compact HXs have been shown to experience water bridging under dehumidification conditions, which greatly impacts HX performance. This research sheds light on the next generation of air-to-refrigerant HXs and aims to address several practical challenges to HX commercialization such as novelty, manufacturing, and operational challenges through the use of comprehensive multi-physics and multi-scale modeling. The novelty of this research is summarized as follows: i. A new, comprehensive and experimentally validated air-to-refrigerant HX optimization framework with simultaneous thermal-hydraulic performance and mechanical strength considerations for novel, non-round, shape- and topology-optimized tubes capable of optimizing single and two-phase HX designs for any refrigerant choice and performance requirement with significant engineering time savings compared to conventional design practices. The framework was exercised for a wide range of applications, resulting in HXs which achieved greater than 20 improved performance, than 20% reductions in size, and 25% reductions in refrigerant charge. ii. Development of a fundamental understanding of performance degradation for HXs with shape- and topology-optimized tubes under typical HX installation configurations in practical applications such as inclined and A-type configurations. New modeling capabilities were integrated into existing HX modeling tools to accurately predict the airflow maldistribution profiles for HXs with shape- and topology-optimized tubes without the need for computationally-expensive CFD simulations. iii. Development of a framework to model and understand the impact of moist air dehumidification on the performance of highly compact HX tube bundles which utilize generalized, non-round tubes. Correlations for Lewis number were developed to understand whether traditional HX dehumidification modeling assumptions remained valid for new HXs with generalized, non-round tube bundles. Such an understanding is critical to accurately and efficiently modeling HX performance under dehumidifying (i.e., wet-coil) conditions.Item COST-EFFECTIVE PROGNOSTICS AND HEALTH MONITORING OF LOCALLY DAMAGED PIPELINES WITH HIGH CONFIDENCE LEVEL(2020) Aria, Amin; Modarres, Mohammad; Azarm, Shapour; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Localized pipeline damages, caused by degradation processes such as corrosion, are prominent, can result in pipeline failure and are expensive to monitor. To prevent pipeline failure, many Prognostics and Health Monitoring (PHM) approaches have been developed in which sensor network for online, and human inspection for offline data gathering are separately used. In this dissertation, a two-level (segment- and integrated-level) PHM approach for locally damaged pipelines is proposed where both of these degradation data gathering schemes (i.e., detection methods) are considered simultaneously. The segment-level approach, in which the damage behavior is considered to be uniform, consists of a static and a dynamic phase. In the static phase, a new optimization problem for the health monitoring layout design of locally damaged pipelines is formulated. The solution to this problem is an optimal configuration (or layout) of degradation detection methods with a minimized health monitoring cost and a maximized likelihood of damage detection. In the dynamic phase, considering the optimal layout, an online fusion of high-frequency sensors data and low-frequency inspection information is conducted to estimate and then update the pipeline’s Remaining Useful Life (RUL) estimate. Subsequently, the segment-level optimization formulation is modified to improve its scalability and facilitate updating layouts considering the online RUL estimates. Finally, at the integrated-level, the modified segment-level approach is used along with Stochastic Dynamic Programming (SDP) to produce an optimal set of layouts for a long pipeline consisting of multiple segments with different damage behavior. Experimental data and several notional examples are used to demonstrate the performance of the proposed approaches. Synthetically generated damage data are used in two examples to demonstrate that the proposed segment-level layout optimization approach results in a more robust solution compared to single detection approaches and deterministic methods. For the dynamic segment-level phase, acoustic emission sensor signals and microscopic images from a set of fatigue crack experiments are considered to show that combining sensor- and image-based damage size estimates leads to accuracy improvements in RUL estimation. Lastly, using synthetically generated damage data for three hypothetical pipeline segments, it is shown that the constructed integrated-level approach provides an optimal set of layouts for several pipeline segments.Item MULTI-VEHICLE ROUTE PLANNING FOR CENTRALIZED AND DECENTRALIZED SYSTEMS(2019) Patel, Ruchir; Herrmann, Jeffrey W; Azarm, Shapour; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Multi-vehicle route planning is the problem of determining routes for a set of vehicles to visit a set of locations of interest. In this thesis, we describe a study of a classical multi-vehicle route planning problem which compared existing solutions methods on min-sum (minimizing total distance traveled) and min-max (minimizing maximum distance traveled) cost objectives. We then extended the work in this study by adapting approaches tested to generate robust solutions to a failure-robust multi vehicle route planning problem in which a potential vehicle failure may require modifying the solution, which could increase costs. Additionally, we considered a decentralized extension to the multi-vehicle route planning problem, also known as the decentralized task allocation problem. The results of a computational study show that our novel genetic algorithm generated better solutions than existing approaches on larger instances with high communication quality.Item Soot Oxidation in Hydrocarbon-free Flames(2015) Guo, Haiqing; Sunderland, Peter B.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There are high uncertainties in the existing models of soot oxidation rates. To ameliorate this, soot oxidation in flames was examined using a novel ternary flame system, advanced diagnostics, and a detailed examination of past studies. The ternary flame system comprises a coflowing propylene/air diffusion flame to generate a steady soot column that flows into a hydrogen ring flame. The soot is thereby oxidized in a region far separated from soot formation, which is unlike any past study of soot oxidation in diffusion flames. Nonintrusive optical diagnostics were developed using a digital color camera to measure temperature and soot volume fraction. These diagnostics were validated using a steady laminar ethylene/air diffusion flame and were then applied to the ternary flame. Also measured in the soot flame were velocity, soot primary particle diameter, and stable species concentrations along an axial distance of 45 mm. Temperatures were between 1500 to 1750 K, and O2 partial pressures were between 10-2 to 10-1 bar. The soot flame was found to be lean, and its OH (with partial pressures between 10-4 to 10-3 bar) was expected to be equilibrated owing to the catalyzed radical recombination in the presence of soot. Soot flux and soot oxidation rates (0.5 to 6 g/m2-s) were determined. Soot burnout was 90% at 55 mm height. New soot oxidation mechanisms for O2 and OH were developed from a large body of published soot oxidation measurements. The resulting O2 mechanism has an activation energy of 195 kJ/mol, and the OH mechanism has a collision efficiency of 0.10. Predictions using the new mechanisms are within ±80% of the present measurements in the ternary flame system.Item Thermal and Hydraulic Performance of Heat Exchangers for Low Temperature Lift Heat Pump Systems(2012) Lee, Hoseong; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The work presented in this dissertation focused on investigating and understanding the hydraulic and thermal design space and tradeoffs for low temperature difference high performance heat exchangers for a low temperature lift heat pump (LTLHP) system, which benefits from a small difference between the condensing and evaporating temperatures of a working fluid. The heat exchangers for the LTLHP application require a larger heat transfer area, a higher volume flow rate, and a higher temperature of heat source fluid, as compared to the typical high temperature lift heat pump system. Therefore, heat exchanger research is critical, and it needs to be balanced between the heat transfer and pressure drop performance of both fluids in the heat exchanger. A plate heat exchanger (PHX) was selected to establish a baseline of a low temperature lift heat exchanger and was investigated experimentally and numerically. The traditional PHX is designed to have the identical surface area and enhancements on both fluid sides for ease of production. However, fluid side heat transfer coefficients and heat transfer capacities can be drastically different, for example, single-phase water versus two-phase refrigerant. Moreover, the PHX needs to have a large cross sectional flow area in order to reduce the heat-source fluid-side pressure drop. In the experimental test, the PHX showed a relatively low overall heat transfer performance and a large pressure drop of the heat source fluid side under LTLHP operating conditions. The CFD simulation was carried out to further improve the potential of the PHX performance. However, there were limitations in the PHX. It was concluded that the PHX was restricted by two main factors: one was a large pressure drop on the heat source fluid-side due to corrugated shape, and the other was low overall heat transfer performance due to the low refrigerant-side mass flux and resulting low heat transfer performance. A concept of a novel low temperature lift heat exchanger (LTLHX) has been developed based on the lessons learned from the PHX performance investigation for the application to the LTLHP. Geometries were newly defined such as a channel width, channel height, channel pitch, and plate flow gap. Two design strategies were applied to the novel heat exchanger development: the flow area ratio was regulated, and plates were offset. The design parameters of the novel heat exchanger were optimized with multi scale approaches. After developing the laboratory heat exchanger test facility and the prototype of the novel LTLHX, its performance was experimentally measured. Then the thermal and hydraulic performance of the novel LTLHX was validated with experimental data. The heat transfer coefficient correlations and the pressure drop correlations of both the water-side and refrigerant-side were newly developed for the novel LTLHX. The overall heat transfer performance of the novel LTLHX was more than doubled as compared to that of the PHX. Moreover, the pressure drop of the novel heat exchanger was drastically lower than that of the PHX. Lastly, the novel heat exchangers were applied to a water source heat pump system, and its performance was investigated with parametric studies.Item Single and Multiresponse Adaptive Design of Experiments with Application to Design Optimization of Novel Heat Exchangers(2009) Aute, Vikrant Chandramohan; Azarm, Shapour; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Engineering design optimization often involves complex computer simulations. Optimization with such simulation models can be time consuming and sometimes computationally intractable. In order to reduce the computational burden, the use of approximation-assisted optimization is proposed in the literature. Approximation involves two phases, first is the Design of Experiments (DOE) phase, in which sample points in the input space are chosen. These sample points are then used in a second phase to develop a simplified model termed as a metamodel, which is computationally efficient and can reasonably represent the behavior of the simulation response. The DOE phase is very crucial to the success of approximation assisted optimization. This dissertation proposes a new adaptive method for single and multiresponse DOE for approximation along with an approximation-based framework for multilevel performance evaluation and design optimization of air-cooled heat exchangers. The dissertation is divided into three research thrusts. The first thrust presents a new adaptive DOE method for single response deterministic computer simulations, also called SFCVT. For SFCVT, the problem of adaptive DOE is posed as a bi-objective optimization problem. The two objectives in this problem, i.e., a cross validation error criterion and a space-filling criterion, are chosen based on the notion that the DOE method has to make a tradeoff between allocating new sample points in regions that are multi-modal and have sensitive response versus allocating sample points in regions that are sparsely sampled. In the second research thrust, a new approach for multiresponse adaptive DOE is developed (i.e., MSFCVT). Here the approach from the first thrust is extended with the notion that the tradeoff should also consider all responses. SFCVT is compared with three other methods from the literature (i.e., maximum entropy design, maximin scaled distance, and accumulative error). It was found that the SFCVT method leads to better performing metamodels for majority of the test problems. The MSFCVT method is also compared with two adaptive DOE methods from the literature and is shown to yield better metamodels, resulting in fewer function calls. In the third research thrust, an approximation-based framework is developed for the performance evaluation and design optimization of novel heat exchangers. There are two parts to this research thrust. First, is a new multi-level performance evaluation method for air-cooled heat exchangers in which conventional 3D Computational Fluid Dynamics (CFD) simulation is replaced with a 2D CFD simulation coupled with an e-NTU based heat exchanger model. In the second part, the methods developed in research thrusts 1 and 2 are used for design optimization of heat exchangers. The optimal solutions from the methods in this thrust have 44% less volume and utilize 61% less material when compared to the current state of the art microchannel heat exchangers. Compared to 3D CFD, the overall computational savings is greater than 95%.Item Simulation and Optimization of Production Control for Lean Manufacturing Transition(2008-08-06) Gahagan, Sean Michael; Herrmann, Jeffrey W; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lean manufacturing is an operations management philosophy that advocates eliminating waste, including work-in-process (WIP) inventory. A common mechanism for controlling WIP is "pull" production control, which limits the amount of WIP at each stage. The process of transforming a system from push production control to pull is not well understood or studied. This dissertation explores the events of a production control transition, quantifies its costs and develops techniques to minimize them. Simulation models of systems undergoing transition from push to pull are used to study this transient behavior. The transition of a single stage system is modeled. An objective function is introduced that defines transition cost in terms of the holding cost of orders in backlog and material in inventory. It incorporates two techniques for mitigating cost: temporarily deferring orders and adding extra capacity. It is shown that, except when backlog costs are high, it is better to transform the system quickly. It is also demonstrated that simulation based optimization is a viable tool to find the optimal transition strategy. Transition of a two-stage system is also modeled. The performance of two simple multi-stage transition strategies is measured. In the first, all of the stages are transformed at the same time. In the second, they are transformed one at a time. It is shown that the latter strategy is superior. Other strategies are also discussed. A new modeling formalism, the Production Control Framework (PCF), is introduced to facilitate automated searches for transition strategies in more complex systems. It is a hierarchical description of a manufacturing system built on a novel extension of the classic queue server model, which can express production control policy parametrically. The PCF is implemented in the form of a software template and its utility is shown as it is used to model and then find the optimal production control policy for a five stage system. This work provides the first practical guidance and insight into the behavior and cost of Lean production control transition, and it lays the groundwork for the development of optimal transition strategies for even the most complex manufacturing systems.Item Transformation Plans for Optimizing Military Vehicle Testing(2007-05-15) Hoy, Timothy W; Herrmann, Jeffrey W; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The U.S. Army Aberdeen Test Center is a leading Department of Defense developmental test center and test range. A majority of the testing conducted at the Aberdeen Test Center is automotive in nature. Due to recent conflicts around the world, the U.S. Armed Services need to field new armored systems rapidly. The rapid deployment of automotive systems has caused the Department of Defense test community and the Aberdeen Test Center in particular to reevaluate and redefine traditional test plans and practices in order to maximize the amount of valid and pertinent data obtained from shortened test schedules. As a result, this thesis studies new transformation plans to provide ways to optimize military test plans. These transformation plans take into account existing military vehicle data from multiple sources including the Aberdeen Test Center's automotive road courses. These transformation plans are not only useful for shortened military tests, but can also be easily employed in developing test plans for private industry customers as well as long term test projects. The benefits in all cases are the same: an optimized test plan for automotive endurance operations.Item Biologically-inspired optimal control(2005-11-14) Shao, Cheng; Hristu, Dimitrios; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Inspired by the collective activities of ant colonies, and by their ability to gradually optimize their foraging trails, this dissertation investigates the cooperative solution of a broad class of trajectory optimization problems with various types of boundary conditions. A set of cooperative control algorithms are presented and proved to converge to an optimal solution by iteratively optimizing an initially feasible trajectory/control pair. The proposed algorithms organize a group of identical control systems by imposing a type of pair-wise interaction known as "local pursuit". The bio-inspired approach taken here requires only short-range, limited interactions between group members, avoids the need for a "global map" of the environment in which the group evolves, and solves an optimal control problem in "small" pieces, in a manner which is made precise. These features enable the application of the proposed algorithms in numerical optimization, leading to an increase of the permitting size of problems that can be solved, as well as a decrease of numerical errors incurred in ill-conditioned problems. The algorithms' effectiveness is illustrated in a series of simulations and laboratory experiments